RF devices and systems typically include one or more RF transceivers for transmitting and receiving wireless signals. FIGS. 1A and 1B illustrate block diagrams of conventional receiver and transmitter circuits of an RF transceiver, respectively. As shown in FIG. 1A, a RF receiver circuit 100 include a RF front end unit 102, coupled to at least one antenna 104, and a signal processing unit 106 coupled to the RF front end unit 102. The RF front end unit 102 includes an impedance matching circuit 110, a low-noise amplifier (LNA) 112, a mixer 114, a local oscillator 116 and a band-pass filter 118. The impedance matching circuit 110 matches the input impedance of the receiver 100 with the impedance of the antenna so that maximum power of a RF signal received by the antenna 104 is transferred to the LNA 112. A primary function of the LNA 112 is to increase the sensitivity of the receiver 100 by amplifying weak signals without introducing significant noise such that the received signals have higher power than the noise in succeeding stages.
From the LNA 112, the RF signal is provided to a mixer 114, which mixes the RF signal with another RF signal provided by the local oscillator 116, to produce an intermediate frequency (IF) signal or baseband signal. The IF or baseband signal is then provided to the band-pass filter 118, which filters out signals that are outside of a predetermined frequency band. The filtered signal is then provided to the signal processing unit to perform additional protocol processing such as, for example, demodulation, media access control (MAC) functions, error correction, digital-to-analog conversion (if necessary), etc. The signal is then sent to additional processing units (not shown) for further application specific processing and/or storage.
As shown in FIG. 1B, the RF transmitter circuit 150 essentially performs the above signal processing functions in reverse order. The RF transmitter circuit 150 includes the signal processing unit 106 discussed above, coupled to a RF back end unit 152, which is coupled to the antenna 104. In alternative systems, the antenna 104 may be replaced with a separate antenna dedicated for transmission, or multiple selectable antennas that can be dynamically selected based on protocol requirements and/or performance characteristics, as is known in the art (e.g., MIMO antennas). The signal processing unit 106 receives baseband signals from an application processing unit (not shown), such as a CPU, and then performs initial processing on the baseband signal so that it may be transmitted. Such initial processing functions can include analog-to-digital conversion (if necessary), packetizing the resulting digital data in accordance with a predetermined protocol (e.g., WiFi/802.11 standard), modulation of the digital data onto an IF carrier signal, etc.
The IF carrier signal from the signal processing unit 106 then passes through another band-pass filter 162 which filters out strong signals having frequencies outside of a predetermined frequency band. The filtered IF signal is then up-converted to a RF signal by mixer 158, which mixes the IF signal with another IF signal provided by the local oscillator 160 to generate the RF signal, using techniques well-known in the art. The resulting RF signal is then amplified by the power amplifier 156 and then transmitted by antenna 104. The impedance matching circuit 154 matches the output impedance of the RF back end unit 152 with the impedance of the antenna 104.
The foregoing provides a general discussion of some basic components or units typically found in conventional RF transceivers. Those of ordinary skill in the art will recognize that various designs and architectures can be implemented for RF transceivers, and in particular, for RF front end units and RF back end units that include additional components or units or omit some of the components or units discussed above. For example, in some receiver circuits, the RF front end can refer to all the circuitry between the antenna up to and including the mixer stage. It consists of all the components in the receiver that process the signal at the original incoming radio frequency (RF), up to and including the mixer, which converts the RF signal to a lower intermediate frequency (IF) so that the signal from the antenna can be transferred to the rest of the receiver at the more easily handled intermediate frequency.
In many modern integrated receivers, however, particularly those in wireless devices such as cell phones and Wifi receivers, the intermediate frequency is digitized; sampled and converted to a binary digital form, and the rest of the processing, such as IF filtering and demodulation, for example, is done by digital filters and one or more digital signal processors (DSP's), as these digital units are smaller, use less power and provide programmability. In this type of receiver the RF front end would be considered as everything from the antenna to the analog to digital converter (ADC) which digitizes the IF signal (not including the antenna but including the ADC). Alternatively, some receivers digitize the RF signal directly, without down-conversion to an IF, so here the front end may merely be a LNA and a RF filter. Those of skill in the art would readily recognize what portions of a receiver constitute a “RF front end” and what portions of a transmitter constitute a “RF back end,” in accordance with various receiver and transmitter designs and architectures, respectively. Generally, as used herein, the term “RF front end” refers to at least a low-noise amplifier (LNA) and may include additional components or units as discussed above, depending on a particular receiver architecture and design. The term “RF back end,” as used herein, will generally refer to at least a power amplifier (PA) and may include additional components or units as discussed above, depending on a particular transmitter's architecture and design.
In many RF applications, such as those utilizing battery-powered, wireless devices configured to communicate in accordance with the 802.11 communication standard protocols (aka, “WiFi”), for example, it is desirable to conserve power as much as possible. By decreasing power consumption, the batteries of such devices require less frequent recharging or replacement, which is more convenient and less costly for users of the devices, and provides a more reliable wireless device.
In a typical low-power WiFi application, for example, the WiFi device is configured to go into its lowest power (sleep) mode between Access Point (AP) beacons that contain Delivery Traffic Indication Map (DTIM) information. As known by those of ordinary skill in the art, the amount of time the WiFi device sleeps is controlled by a DTIM setting. For example, if an AP beacon interval is set to be 100 milliseconds (ms) and the DTIM setting is set to 3, then the low power WiFi device wakes up every 300 ms to receive a beacon and check if any traffic is available for it to receive.
During the sleep period in which the WiFi device is in its lowest power mode, the RF front end and RF back end units' receive (Rx) and transmit (Tx) functions, respectively, are both disabled for predetermined periods of time. Even in this sleep mode, however, the RF transceiver, comprising a WiFi signal processing unit and RF front and back end units, as described above, consumes a non-negligible amount of power, which over time will unduly drain a battery pack. As an example, the WiFi signal processing unit may include a WiFi Media Access and Control (MAC) unit and a radio Application Specific Standard Product (ASSP) unit, which are known in the art. Such a WiFI signal processing unit might consume 170 μW, while the RF Power Amplifier (PA) in the RF back end unit and the Low Noise Amplifier (LNA) in the RF front end unit might together consume 54 μW, for example, during sleep mode. Thus, in this example, even during sleep mode (a.k.a., “idle mode”), a conventional low-power WiFi device may still have a total power consumption of 224 μW (excluding any additional power lost due to power supply inefficiencies). This power consumption is a drain on the battery pack of the WiFi device.
In addition to power consumption by the RF transceiver, typical WiFi devices must power on a host processor that controls the RF transceiver and performs necessary network and application processing functions (e.g., functions above the MAC layer) each time the RF transceiver transmits or receives a signal. The powering on of the host processor in this fashion results in significant power consumption by the WiFi device.
Thus, there is a need for a method and system that can provide further reductions in power consumption in low-power RF applications.